Moore filed a suit yesterday at Los Angeles superior court in which he says the Weinsteins and an affiliated firm named the Fellowship Adventure Group hid profits despite an agreement to split financial proceeds from the 2004 anti-George W Bush polemic 50/50. The lawsuit accuses brothers Bob and Harvey Weinstein of using "Hollywood accounting tricks" and "financial deception" to cheat Moore out of a chunk of his share of profits from the film, the highest-grossing documentary of all time.

"An independent auditor came in and discovered that the Weinsteins had re-routed at least $2.7m that belonged to Michael Moore from Fahrenheit 9/11," said the film-maker's lawyer Larry Stein in a statement. "This is the first time Michael Moore has ever sued anyone in his 20-year career as a film-maker. That should be some indication about how serious this is."

The suit comes as a shock because Moore and the Weinsteins have always appeared joined at the hip in their film-making endeavours. Since Fahrenheit 9/11 they have partnered on all Moore's documentaries, including 2007's Sicko and 2009's Capitalism: A Love Story. Fahrenheit 9/11 was also the catalyst for the brothers to quit Miramax, the company they founded in 1979, and form current venture The Weinstein Company (in 2005). The departure followed a spectacular row with Miramax owners Disney over Moore's documentary, which the company refused to release due to its political content.

"It's very sad it had to come to this. Michael believes the Weinsteins have been a force for good when it comes to championing independent film – but that does not give them the right to violate a contract and take money that isn't theirs," added Stein. "The $2.7m is just the floor of what we believe is owed. When this goes to discovery I wouldn't be surprised if the amount of what was taken goes much, much higher."

Moore's suit is reportedly a last-resort action which follows extended negotiations taking place over six months between the two sides over proceeds from Fahrenheit 9/11.

Among the details of the suit are allegations that the Weinsteins deducted $1.2m from profits for advertising costs which they did not incur, in contradiction of the agreement, and hired a private jet to carry a single passenger to Europe. The brothers fiercely deny Moore's assertions and dispute the suggestion that they owe the film-maker any money.

"The Weinsteins have paid everything they should have paid," lawyer Bert Fields told the Hollywood Reporter. "Mr Moore has received a huge amount of money from this film and we believe he is overreaching. He should be ashamed of himself."

The suit does not necessarily spell the end for the Moore/Weinstein relationship, however, as Hollywood has a history of breaking up and making up over financial issues. In 2005 Peter Jackson sued Warner Brothers offshoot New Line for an unspecified sum in lost profits from fantasy trilogy The Lord of the Rings. The studio's chairman, Bob Shaye, later said that the Kiwi film-maker was banned from working on New Line projects, including a potential adaptation of JRR Tolkien's book The Hobbit. Two and a half years later, Shaye was making conciliatory noises following the suit's resolution. Next month, Jackson will start filming The Lord of the Rings prequel The Hobbit for Warner.